Reinforcement device for supporting structures

ABSTRACT

The ends of carbon plates reinforcing supporting elements, such as concrete beams, are divided into at least two splines having approximately the same thickness and are glued in the appropriate retaining slots of a terminal element. The splines form an angle in relation to each other. This assembly is then glued to the traction side of the supporting element, whereby the carbon plates are directly prestressed by the terminal elements in relation to the supporting element. The terminal element can be inserted into an appropriate groove in the supporting element or glued directly on the surface of the supporting element and/or doweled, optionally by using a transverse tensioning device.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a reinforcing device as well as amethod for reinforcing beams.

When rehabilitating supporting structures in existing buildings, thesupporting structures often are to be adapted for new load cases thatexceed the former dimensions. In order to avoid replacing a supportingstructure completely in such cases, methods and devices for reinforcingsuch an existing supporting structure have been found. Such supportingstructures can be walls of conventional design made of brick, reinforcedconcrete walls or beams, or beams made of wood, plastic, or steel, forexample.

Reinforcement of such supporting structures with steel plates addedlater has been known for a long time. The steel plates, namely strips ofsheet steel or steel panels, are glued to one or both sides of thesupporting structure, preferably on the side of the supporting structuresubjected to tension. The advantage of this method is that it can beimplemented relatively quickly, but the method imposes strictrequirements on the adhesive. In other words, the preparation of theparts and the performance of the adhesion process must take place underprecisely defined conditions to achieve the desired effect. Problems,and especially corrosion problems, arise when supporting structures suchas bridge beams are to be reinforced in this manner in the open. Becauseof the relatively high weight and the production of such steel panels,the maximum length that can be used is limited. Likewise, for reasons ofspace, installation in closed spaces can be problematic when the rigidsteel panels cannot be transported into the space in question. Inaddition, the steel plates must be pressed against the supportingstructure to be reinforced until the adhesive sets in “overhead”applications. This also results in high cost.

It is known from French Publication 2 590 608 to use tensioning means inthe form of strips of metal or fiber-reinforced plastic with anchors atthe ends. In this embodiment, however, there is no flush connectionbetween the tensioning means and the supporting structure. Instead, aconnection with the supporting structure is provided only in the two endanchoring points of the tensioning means. Clamping means of this kindare conventionally included when planning the supporting structure,because retrofitting is practically impossible or can be done only atvery high cost, since corresponding channels in the supports must beprepared for the clamping means.

Recently, carbon panels (CFK panels) have been glued to the tensionedsides of the supporting structure and, thus, the carrying capacity ofsuch structures is subsequently improved by increasing the supportingresistance and ductility. Advantageously, the simple and economicalapplication of such panels, which have a higher strength than steelpanels with a far smaller weight, is provided, and the panels aresimpler to install. The corrosion resistance is also better so that suchreinforcements are also suitable for reinforcing supporting structuresin the open. However, the end anchoring of the panels has proven to beparticularly problematical. The danger of the panels coming loose isparticularly great in this areas and there is a problem in that theforce is introduced from the end of the panel into the beam.

A solution is this regard is known from international publicationWO96/21785; here, a bore that runs at an obtuse angle or a wedge-shapedrecess is made in the beam in which the ends of the CFK panels areinserted and pressed against the beam, possibly by clamps, loops,plates, etc. This results in an improvement in loosening behavior and animproved initiation of the force from the beam into the panel. However,such CFK panels are glued without pretensioning, in other wordsflexibly, to the beam. As a result, much of the reinforcing potential ofthese panels is not utilized, since panels begin to provide support onlyafter they exceed the basic load, in other words under stress from theuseful load itself.

In order to utilize the panels better, the idea has arisen of gluingthem pretensioned to the beam. One known solution 1 in this regardprovides that short steel plates are glued to the ends of the CFK panelson both sides. The steel plates are then pulled apart and the CFK panelsare pretensioned, and this pretensioned arrangement is glued to the beamto be reinforced. After the glue dries, the panels are pressed at theends against the beams by plates, loops, etc. and the ends are then cutoff with the steel plates. This method, however, is very expensive andcannot be used in all applications. The method of anchoring the panelends described above is also not suitable for pretensioning at buildingsites.

Hence, the goal of the present invention is to provide a CFK reinforcingpanel in which the introduction of force from the beam into the endstakes place in such fashion that separation becomes practicallyimpossible and which is also suitable for pretensioning.

This goal is achieved by splitting the ends of a CFK panel into at leasttwo and preferably three or more end; strips. In this way, the surfacefor connection to an end element is increased considerably. As a result,there is a good initiation of the force into the ends of the CFK panelwhich can also be pretensioned in simple fashion by such an end element.The end element in block form can be either inserted into a depressionin the beam or, in the preferred embodiment, with a wedge-shaped splitwith a flat or rough bottom, can also be glued and/or doweled or simplybolted flush to the beam. It is this embodiment that is preferablysuited for pretensioning which preferably takes place directly throughthe beam part. For example, this can be done by tensioning against afitting inserted into the beam.

The splitting of the ends of the CFK panels preferably takes the formeither of strips on top of one another or strips that are side-by-side,or in a combination of these two versions.

The ends of the CFK panels can advantageously be split at the buildingsite itself to the required length and dimensions. This makes thissystem highly universal for the reinforcement of practically any beam,and the system can be employed with or without pretensioning.

The invention is described in greater detail below with reference to thefigures in the enclosed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section through a beam with a CFK panel accordingto the invention attached to its underside;

FIG. 2 shows a cross section through the head part of the CFK panel inFIG. 1;

FIG. 3 shows a cross section through the end of a CFK panel according toFIGS. 1 and 2;

FIG. 4 shows a cross section through a beam with an additional CFK panelaccording to the invention mounted on the underside;

FIG. 5 shows a cross section through the head part of the CFK panelaccording to FIG. 4;

FIG. 6 shows a schematic cross section through an alternative head partof a CFK panel according to the invention;

FIG. 7 is a schematic cross section through an additional alternativehead part of a CFK panel according to the invention; and

FIG. 8 is a top view of another alternative embodiment of the head partof a CFK panel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a cross section through a beam 1 to be reinforced. The endsof the CFK panel 2 used for this purpose are inserted according to theinvention in elements, in this case anchor heads 3 and 4. Anchor heads 3and 4 can be inserted into milled or pointed recesses of beam 1 as shownin this figure. CFK panel 2 is connected with beam 1 over part or all ofthe area by a layer of adhesive 5 and the anchor heads 3 and 4 are gluedto it as well. In addition, anchor heads 3 and 4 can be connected withthe beam by a transverse clamping device 6, shown here simplyschematically, resulting in an improved direction of the force throughthe anchor heads 3 and 4 from the CFK panel 2 into the beam 1. Thistransverse clamping device 6 can be for example, a threaded rod or dowelguided through the beam 1 and the anchor heads 3 and 4.

The reinforcing device composed of the CFK panel 2 and the anchor heads3 and 4 can also be simply pretensioned as shown schematically on theright-hand side of FIG. 1. For this purpose, for example, an angularfitting 7 can be attached to the underside 1 of the beam. This fittingis gripped by a tension rod 8 connected at one of its ends by the anchorhead 4. It is advantageous to provide both of the anchor heads 3 and 4with such a tensioning device for pretensioning. The clamping device ismounted before gluing and can be removed again after the adhesive curesbetween the CFK panel 2 or the anchor heads 3 and 4 and the beam 1.

FIG. 2 shows a cross section through one of the anchor heads 3. In theanchor head 3, in the form of a parallelepiped, preferably three guideor retaining slots 9 are provided one above the other. These slots canaccept the end of CFK panel 2 after it is divided into three tabs 2′ asshown in FIG. 3.

Retaining slots 9 are spread upward and downward wedgewise and havetransverse bores 10. These bores 10 provide additional anchoring pointsfor the adhesive that connects the strips 2′ of the CFK panel 2 with theretaining slots 9. In this way, the introduction of tensile forces fromthe beam 1 through the anchor head 3 into the CFK panel 2 isadditionally improved. The great advantage, however, lies in splittingthe end of the panel 2 into the strips 2′. This splitting is preferablyperformed in the fiber direction of the panels and advantageouslyresults in an increase in gluing area without the strength properties ofthe CFK panel 2 being adversely affected.

In the present example with three strips 2′, the gluing area isincreased six times with respect to a conventional panel that is simplyglued at its end to the beam, and is increased three times over theknown solution with a wedge-shaped recess in the beam and adhesionbridges.

In order to prevent bending or tearing in the outlet area of the anchorhead 3 of the CFK panel 2 by transverse forces that result from thewedge-shaped or arcuate arrangement of the retaining slots 9, atransverse reinforcement 11 which is only indicated schematically inFIG. 2 is provided. For example, this transverse reinforcement 11 can beprovided by threaded rods guided through matching bores in anchor head 3and tightened by nuts. Thus, any shear stress peaks in the outlet areaof anchor head 3 are subject to overpressure and higher shear stressesare permitted in this zone.

In addition, a threaded bore 12 is provided in anchor head 3, forexample, into which bore a pretensioning device can be screwed as shownschematically in FIG. 1.

FIG. 3 shows, as already mentioned, one end of the CFK panel 2 with theend of the panel split into three strips 2′. The CFK panel can be splitby conventional means following cutting to length, to the desired lengthand the; desired number of equally thick strips 2′. Cutting may beperformed, for examples by a plane or knife. It, is advantageous in thisregard that relatively low requirements are imposed on the quality ofthe splitting; the important aspect is the division into the correctnumber of strips 2′ to achieve the increase in area for the connectionto the anchor head 3.

FIG. 4 shows a cross section through a beam 1 with a reinforcing deviceaccording to the invention mounted on the underside (tension side),consisting of a CFK panel 2 with anchor heads 3 and 4 attached to theends. Anchor heads 3 and 4 are so designed that the CFK panel 2 emergespractically at the level of adhesive layer 5 from the anchor heads 3 and4 and the latter, therefore, must not be depressed in the underside ofbeam 1 but must also be glued flush to the underside. Of course, thetransverse tensioning devices 6 shown in FIG. 1 can also be mounted hereto produce a higher pressure and thus a higher tensile strength of theconnection between anchor heads 3 and 4 and the underside of the beam.Likewise, these anchor heads 3 and 4, like the embodiment alreadydescribed above, can be pretensioned simply.

FIG. 5 shows a cross section through an anchor head 3 and thecorresponding arrangement of the holding slots 9. The bottom slot 9′ isparallel to the outside wall 3′ of the anchor head 3, resting on beam 1,and the other slots 9 are located at an acute angle pointing outward inthe form of a fan. This arrangement offers the same advantages asalready described as a result of the increase in the gluing surface ofthe CFK panel 2 and also allows the flush application of anchor heads 3and 4 as well without additional recesses in beam 1. These anchor heads3 and 4 also have transverse reinforcing means 11, as shownschematically in FIG. 2, to avoid bending or tearing of anchor heads 3and 4 in the area where the CFK panel 2 emerges.

As material for the anchor heads 3, 4, metal which exhibits highstrength, ease of machining, and good force initiation properties issuitable, as is plastic, especially when corrosion is expected to behigh.

FIG. 6 is a schematic view of another embodiment of the reinforcingdevice according to the invention. The end of, the CFK panel 2 is splithere into two superimposed strips 2′ which come to rest on the outsideof a wedge-shaped anchor head 14. There they can be connected to thesurface of the anchor head 14 by gluing.

In another embodiment according to the invention, the split strips 2′ atthe end of the CFK panel 2 are held in an anchor head composed of plates15 located parallel one on top of the other as shown in a lengthwisesection in FIG. 7. Here a screw connection 16 can be advantageouslyemployed to press the plate 15 and the strips 2′ against one another.

FIG. 8 is a top view of another embodiment of the end of the CFK panel2. Here, the strips 2′ are not shown one on top of the other but arelocated laterally side by side. Here again, the split is preferably madein the fiber direction of the CFK panel 2.

The reinforcing devices according to the invention are especially suitedfor rehabilitating existing concrete beam structures, such as ceilingsor bridge beams. However, they can also be used for all knownapplications of conventional CFK panels, for example masonry and woodensupporting structures. The ease with which they can be pretensionedpermits a greater utilization of the strength properties of the CFKpanels than in known methods. In addition, pretensioning means that onthe tension side of an existing supporting element, pre-pressing takesplace that is advantageous, for examples in bridge beams.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. Reinforcing device for supporting structures comprising: a carbonpanel, at least one end of the carbon panel being split into at leasttwo strips, and an end element in which said at least one endterminates, wherein the strips are inserted at least partially intoretaining slots of the end element that are located wedgewise relativeto one another.
 2. Reinforcing device according to claim 1 wherein theend element in the vicinity of the outlet of the carbon panel has atleast one transverse reinforcement located transversely to an outletdirection.
 3. Reinforcing device according to claim 2, whereinreinforcement is a threaded rod.
 4. Reinforcing device according toclaim 1 wherein each of two ends of the carbon panel terminates in anend element.
 5. Reinforcing device according to claim 1 wherein saidretaining slots of the end element have a rough or corrugated surface.6. Reinforcing device according to claim 1 wherein bores orientedtransversely to the surface of the panel are located in the end elementin the vicinity of said retaining slots.
 7. Reinforcing device accordingto claim 1 wherein the end element has a threaded bore opposite theoutlet of the carbon panel.
 8. Reinforcing device according to claim 1wherein the retaining slots are located wedgewise in the end elementsuch that a lowest retaining slot is parallel to the outlet direction ofthe carbon panel and each of the other retaining slots is locatedfanwise with an increasing angle from the outlet opening.
 9. Reinforcingdevice according to claim 1, wherein the end element comprises at leasttwo spaced apart components to form slots into which the strips are atleast partially inserted.
 10. Reinforcing device for supportingstructures comprising: a carbon panel, at least one end of the carbonpanel being split into at least two strips, and an end element in whichsaid at least one end terminates and having slots to receive the strips,wherein the end element is a parallelepiped made of metal or plastic.11. Method for reinforcing supporting elements with reinforcing devicescomprising: cutting carbon panels to an appropriate length, separatingor splitting each panel at at least one end into at least two strips ofapproximately the same thickness or width, bringing the at least one endinto a connection with an end element to form an arrangement, and gluingthe arrangement to a tension side of a supporting element to bereinforced, wherein the strips of approximately the same thickness orwidth are introduced into separate retaining slots of the end elementwhich are arranged fanwise with respect to one another and glued inplace or soaked with an adhesive.